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Synonyms for Strain (same or very similar meaning)

WordNet sense 1 (difficulty that causes worry or emotional tension):

WordNet sense 2 ((psychology) nervousness resulting from mental stress):
mental strain, nervous strain

WordNet sense 3 ((biology) a group of organisms within a species that differ in trivial ways from similar groups):
form, variant, var.

WordNet sense 4 (a special variety of domesticated animals within a species):
breed, stock

WordNet sense 5 (a succession of notes forming a distinctive sequence):
air, line, melody, tune, melodic line, melodic phrase

WordNet sense 6 (the general meaning or substance of an utterance):

WordNet sense 7 (test the limits of):

WordNet sense 8 (become stretched or tense or taught):

WordNet sense 9 (separate by passing through a sieve or other straining device to separate out coarser elements):
sieve, sift

WordNet sense 10 (remove by passing through a filter):
filter, filtrate, filter out, separate out

WordNet sense 11 (rub through a strainer or process in an electric blender):

WordNet sense 12 (use to the utmost; exert vigorously or to full capacity):

WordNet sense 13 (to exert much effort or energy):
reach, strive

WordNet sense 14 (an effortful attempt to attain a goal):
pains, nisus, striving

WordNet sense 15 (an intense or violent exertion):

WordNet sense 16 (the act of singing):

WordNet sense 17 (alter the shape of (something) by stress):
deform, distort

WordNet sense 18 (cause to be tense and uneasy or nervous or anxious):
tense up

From the ODE community, based on WordNetadd/edit