Acronym for "Terrible Woman Instigating Trouble". Most often a female friend or co-worker who in an obsessive covert manner sabotages the relationship of a committed couple to oust one partner for her to permanently replace. May have issues (+/-) of mental or physical impairment typically found to be undesirable in a mate.
"Honey, have you noticed our friend Swethoggah giving you "the look"? S/he drops in so often I sometimes think s/he doesn't want you and I to spend time alone. We should start being not so available because s/he is acting like a T.W.I.T."