מָר
From LSJ
κάλλιστον ἐφόδιον τῷ γήρᾳ ἡ παιδεία (Aristotle, quoted by Diogenes Laertius 5.21) → the finest provision for old age is education
English (Strong)
or (feminine) marah; from מָרַר; bitter (literally or figuratively); also (as noun) bitterness, or (adverbially) bitterly: + angry, bitter(-ly, -ness), chafed, discontented, X great, heavy.