English
subrational
From sub- + rational.
Proto-Indo-European *upó ‘up; from below’
Proto-Italic *supo ‘under’
Latin sub ‘under, beneath, below’
English sub-
Proto-Indo-European *h₂er- ‘to fit, to fix, to put together, to slot’
Latin reor ‘to compute’
Latin ratio ‘reason’
Latin rationalis ‘of or belonging to reason, rational, reasonable’
Old French rationel
English rational
Today it means
adj Below or not fully rational; almost logical or reasonable.
Language periods are conventional ranges, not dates for this word.
Etymograph / subrational