Diligent

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Middle English: via Old French from Latin diligens, diligent- ‘assiduous’, from diligere ‘love, take delight in’.

wiktionary

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From Middle English diligent, from Old French diligent, from Latin dīligēns(“careful, attentive, diligent”), present participle of dīligō(“to love, esteem much, literally to choose, select”), from dī-, dis-(“apart”) + legō(“to choose”); see elect and select.

etymonline

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diligent (adj.)

"constant in effort to accomplish what is undertaken," mid-14c., from Old French diligent (14c.) and directly from Latin diligentem (nominative diligens) "attentive, assiduous, careful," present-participle adjective from diligere "single out, value highly, esteem, prize, love; aspire to, be content with, appreciate," originally "to pick out, select," from dis- "apart" (see dis-) + legere "choose, gather," from PIE root *leg- (1) "to collect, gather," with derivatives meaning "to speak (to 'pick out words')." Related: Diligently.