deviation vs driftage

deviation and driftage both are nouns.

Word	Noun	Adjective	Verb	Adverb
deviation	Yes	No	No	No
driftage	Yes	No	No	No

As nouns, driftage is a hyponym of deviation; that is, driftage is a word with a more specific, narrower meaning than deviation:

deviation: a variation that deviates from the standard or norm
driftage: the deviation (by a vessel or aircraft) from its intended course due to drifting

Other hyponyms of deviation include discrepancy, variance, variant, flection, flexion, inflection.

deviation (noun)	driftage (noun)
deviate behavior	the deviation (by a vessel or aircraft) from its intended course due to drifting
a turning aside (of your course or attention or concern)
the error of a compass due to local magnetic disturbances
the difference between an observed value and the expected value of a variable or function
a variation that deviates from the standard or norm