Painful means causing hurt in the body or in the feelings. A painful injury, a painful memory, painfully slow.
It covers both without any change of word, which English does not do for every such pair. Painfully as an intensifier means to an uncomfortable degree — painfully obvious, painfully thin. Note pain; and that the Latin behind it is poena, a penalty, so pain was originally punishment.
1adjectivepainfulCausing hurt in the body or in the feelings.
“The injection was quick but quite painful.”
synonyms: sore, distressing
painful is a quality of causing hurt.
Pain plus -ful, from Old French peine, from Latin poena, a penalty. Penalty, punish and penitent come from the same punishment.
Middle English
paynful
English, today
painful
From Middle English paynful, peinful, peynful, paynefull, peynefull, equivalent to pain + -ful. Compare Danish pinefuld (“painful”).
Etymology from Wiktionary, CC BY-SA