infeasible

From in- +‎ feasible. Cognate to French infaisable.

infeasible (comparative more infeasible, superlative most infeasible)

1. not feasible

   Antonym: feasible

Usage varies between infeasible, unfeasible, and “not feasible” – all are synonymous, but usage varies regionally and over time, and unfamiliar usage is often jarring or sounds wrong. Today infeasible is somewhat more common in American usage, though traditionally unfeasible was more common, being surpassed by infeasible in the late 1970s (in both America and Britain). Of these, infeasible is etymologically pure – formed of French/Latin roots – and cognate to French infaisable, while unfeasible is hybrid, combining Germanic un- with Latinate feasible.[1]