understanding, comprehension

to understand, to comprehend

toil, hardship / worry, anxiety

toilsome, painstaking / worrisome

to toil, to work hard / to worry

mathematics (field of study)

he / distal demonstrative, something far off removed from both speaker and listener: that / boyfriend

distal demonstrative, something far off removed from both speaker and listener: that, yon / particularly, male personal third person pronoun: he / by extension from he: boyfriend

he; boyfriend

(mathematics) pure mathematics