'Fulsome', 'ram', and 'woolly' make up an unpleasant chain of associations that amount to a set of cacophonous variations on the theme of "Ba, ba, black sheep."
Othello uses the word 'fulsome' at the point of his linguistic collapse:
35 Lie with her?
lie on her? We say lie on her,
36 when they belie her. Lie with her!
['Zounds,] that's
37 fulsome! Handkerchief --
confessions -- handkerchief!
(Oth.
4.1.35-37)
The word occurs on four other occasions in the collocations 'fulsome wine' (Ri3 5.3.132), 'fulsome dust'( KiJ. 3.4.32), 'fulsome ewes' (MeV 1.3.86), and 'fat and fulsome' (TwN. 5.1.109). The phrase 'fulsome ewes' in The Merchant of Venice occurs in Shylock's justification of taking interest on the basis of Jacob's practice with Laban's sheep:
78 When Laban
and himself were compremis'd
79
That all the eanlings which were streak'd and pied
80
Should fall as Jacob's hire, the ewes being rank
81
In end of autumn turned to the rams,
82
And when the work of generation was
83
Between these woolly breeders in the act,
84
The skillful shepherd pill'd me certain wands,
85
And in the doing of the deed of kind,
86 He stuck them up before the fulsome
ewes,
87
Who then conceiving did in eaning time
88
Fall parti-color'd lambs, and those were Jacob's.
89
This was a way to thrive, and he was blest;
90
And thrift is blessing, if men steal it not. (MeV. 1.3.78-90)
The passage rests on a deep resistance to tampering with whatever counts as "natural" reproduction. Jacob uses artificial means to produce a kind of hybrid ("streak'd and pied"), and from this it is only one step to the entirely artificial generation of money from money.
'Fulsome' in this passage seems to refer quite literally to the ewes at the point of being mounted or "rammed"--an image Shakespeare also uses in The Rape of Lucrece: "Rude ram, to batter such an ivory wall!"(464). And that appears to be precisely the meaning Othello intends as he envisages Desdemona's infidelity. The connection is strengthened by looking at 'woolly'. The only other occurrence of this word comes in Titus Andronicus, when Tamora, the Queen of the Goths, invites Aaron the Moor to make love to her. This is a crossing of racial boundaries, seen here as the encounter of barbarians from the North (Goth) and the South (Moor):
30 Madam, though
Venus govern your desires,
31 Saturn is dominator over mine:
32 What signifies my deadly-standing
eye,
33 My silence, an' my cloudy
melancholy,
34 My fleece of woolly hair that
now uncurls,
35 Even as an adder when she doth
unroll
36 To do some fatal execution?
37 No, madam, these are no venereal
signs.
38 Vengeance is in my heart, death in
my hand,
39 Blood and revenge are hammering in
my head.
(
Tit. 2.3.30-39)
The comparison of the hair of Africans to wool is as old as Herodotus. Shakespeare draws on it here, but he also sees woolly hair as "venereal sign": as Aaron turns from love to revenge, his hair "uncurls". So the association of Africans with sexual passion is not far from this image, and Aaron is a "woolly breeder." This chain of association erupts most spectacularly in Iago's obscene shout to Brabantio: "Even now, now, very now, an old black ram / Is tupping your white ewe" (Oth. 1.1.88-89). But something very much like this image also seems to underlie Othello's use of 'fulsome.'
A scene in As You Like It provides a bridge between the passages discussed so far. The shepherd Corin and the fool Touchstone discuss the relative merits of court and country. Corin speaks for the country and says that "the greatest of my pride is to see my ewes graze and my lambs suck." But Touchstone turns this scene of innocence into a scene of sexual disgust:
78 That is
another simple sin in you, to bring
79 the ewes and the rams together, and
to offer to get
80 your living by the copulation of
cattle; to be bawd to a
81 bell-wether, and to betray a
she-lamb of a twelvemonth
82 to a crooked-pated old cuckoldly
ram, out of
83 all reasonable match.
(AYL 3.2.78-83)
This is certainly close to Iago's "old black ram."
It is also worth noting that Touchstone thinks of the union of ram and she-lamb
as an "unreasonable match" or mésalliance--precisely the theme that
is so prominent in Othello.[1]
[1] While 'fulsome' and 'woolly' are rare words by any count, 'ram' is not uncommon. There are sixteen occurrences of the lemma in twelve works. There are actually three different lemmata here: the word for the animal including the sign of the Zodiac, the word for a battering ram (which may or may not be etymologically related), and the verb 'ram'. Semantically, the three lemmata run into each other, and Shakespeare's association of the word with repulsive sexuality depends on this conflation.