Felicity
late Middle English: from Old French felicite, from Latin felicitas, from felix, felic- ‘happy’.
wiktionary
From Middle English felicite(“bliss, happiness, joy; delight, pleasure; a source of happiness; good fortune; prosperity; well-being; of a planet: in an influential position”)[and other forms], [1] borrowed from Old French felicité (modern French félicité(“bliss, happiness; felicity”)), from Latin fēlīcitātem, the accusative singular of fēlīcitās(“fertility, fruitfulness; happiness, felicity; good fortune; success”), from fēlix(“happy; blessed, fortunate, lucky; fertile, fruitful; prosperous; auspicious, favourable”) (ultimately from Proto-Indo-European *dʰeh₁(y)-(“to nurse, suckle”)) [2] + -itās (a variant of -tās( suffix forming nouns indicating a state of being)).
etymonline
felicity (n.)
late 14c., "happiness; that which is a source of happiness," from Old French felicite "happiness" (14c.), from Latin felicitatem (nominative felicitas) "happiness, fertility," from felix (genitive felicis) "happy, fortunate, fruitful, fertile" (from suffixed form of PIE *dhe(i)- "to suck," with derivatives meaning "to suckle, produce, yield").
A relic of Rome's origins as an agricultural community: that which brings happiness is that which produces crops. Compare pauper (see poor (adj.)) "poor, not wealthy," literally "producing little." The meaning "skillful adroitness, admirable propriety" is attested from c. 1600.
