An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

1a) A state of mind in which one is troubled; worry, anxiety, or concern; a cause or object of worry, anxiety, concern, etc.
1b) Serious attention; solicitude; heed; caution.
2a) To be concerned or solicitous; have thought or regard.
2b) To be concerned or have a special preference (Dictionary.com).

M.E., from O.E. caru, cearu "sorrow, anxiety, grief," cognate with Gothic kara, O.H.G. chara lament; M.En. caren, O.E. cearian, carian "be anxious, grieve."

Timâr "care, attendance on the sick; custody; sorrow;" Mid.Pers. têmâr "care; grief"

1) Cautious in one's actions.
2) Taking pains in one's work; exact; thorough.
3) (of things) Done or performed with accuracy or caution (Dictionary.com).

→ care; + -ful, a suffix meaning "characterized by; full of; able to;" → full.