younger brother, faithful service to elders
弟 centers on the junior male sibling relationship: a younger brother, and by extension the respectful, faithful service expected toward elders.
弟 originally depicted a cord or thong wrapped around a weapon or tool, later borrowed for 'younger brother' and extended to ideas of order and respect toward elders.
The top stroke 丿 looks like a protective older sibling, and the inner part 弚 resembles a smaller figure with a bowing head—a younger brother showing respect.
For テイ, imagine a younger brother taking a tea break with his elder: tea -> テイ, and the faithful service is shown by serving tea.
younger brother; little brother; kid brother
brothers and sisters; siblings
pupil; disciple; adherent; follower; apprentice; young person; teacher's student-helper
cousin (male)
brother-in-law (spouse's younger brother or younger sister's husband)
teacher and student
brother-in-law; stepbrother; sworn brother
cousin (younger male)
one's younger brother
children; sons; children and younger brothers
sworn younger brother; junior male peer (in a club, group, etc.)
youngest brother
biological younger brother
younger brother and sister
senior pupil (of the same master); senior disciple; senior student; senior member
sworn brother; buddy; pal
second cousin
apprentice
favorite pupil; favourite pupil; teacher's pet
disciple; pupil; follower