(Translated by https://www.hiragana.jp/)
back - Wikivortaro

I. (n.) (of body, knife, book, hand, etc.) dorso (cf. fundo);

(opposite of front) reverso;
(rear) dopo, dopajo.
at the back - dope.
back to back - dorso an dorso.
lower back - lumbo.
break one's back - ruptar la spino.
turn one's back - turnar la dorso (ad ulu).
set the back of (di ulu, ulo) to (ulu, ulo) - adosar.
lean one's back - adosar su.
back of a seat - dors-apogilo.
relating to the back - dorsala.

II. (adj.) dopa;

(remote) fora; distanta.
back shop - dopa butiko.
back door - dopa pordo.

III. (adv.) dope; retro;

(remote) fore.
(in arrears) tarda, nepagita;
(earlier) frua;
to call back - rivokar, retrovokar.
to come back - rivenar, retrovenar.
to flow back - retrofluar.
to give back - retrocedar.
to hold back - represar.
to keep back - ditenar.
to throw back - retrojetar.
to go back - regresar, retroirar, rivenar (ad).
to be back - esar retroveninta (de).
to turn back - (feathers, hair) arufar; (change direction again) riturnar (su, ulo); retroirar, retromarchar.
back of me (US) - dop me.

IV. (prefix) ri., retro.

V. (v.) (intr.) retroirar, retromarchar;

(cause to back) retroirigar (a boat, etc.);
(strengthen, sustain) fortigar, sustenar, apogar;
(bet) pariar;
(second, back up a motion, resolution) sekondar;
(a warrant, etc.) vistar;
(com. bills) indosar.