From Middle English throwe, perhaps from Old English þrēa, thrawu (“threat”). This definition is lacking an etymology or has an incomplete etymology. You can help Wiktionary by giving it a proper etymology.
throe (plural throes)
- A pang, spasm.
- 1819, Percy Shelley, The Masque of Anarchy:
- A hard struggle.
Derived terms 
- (transitive) To put in agony.
- (intransitive) To struggle in extreme pain; to be in agony; to agonize.
Part or all of this entry has been imported from the 1913 edition of Webster’s Dictionary, which is now free of copyright and hence in the public domain. The imported definitions may be significantly out of date, and any more recent senses may be completely missing.