夫 is 大 — a standing adult — with a stroke through the head: the hairpin. At twenty, a man's hair was bound with a pin in the capping ceremony. The pin made the man; 夫 is adulthood you can see.
丈夫 husband, 夫妻 married couple, 大夫 (dàifu) — doctor, from an old court title. 功夫 kung fu is 'time and skill invested': in Chinese, mastery of anything is 功夫, and 下功夫 means putting in the hours.
An adult 大 with a hairpin — capped, grown, a MAN, a HUSBAND.
大夫 read dàifu means doctor; read dàfū it's an ancient minister. Getting the tone wrong sends your physician to the Zhou-dynasty court.