determine, fix, establish, decide
定 centers on making something firm and settled: determining a course, fixing a value, establishing a rule, or deciding an outcome. All its meanings share the idea of bringing something from an unsettled state into a stable, definite one.
plans; arrangement; schedule; program; programme; expectation; estimate
establishment; creation; posing (a problem); setting (movie, novel, etc.); scene
limit; restriction
decision; determination
designation; specification; assignment; appointment; pointing at
specific; particular; designated; special
stability; steadiness; consistency; equilibrium; balance; composure
fixed period; fixed term
fixing (in place); being fixed (in place); securing; anchoring; fastening down
decision; settlement; confirmation; establishment
authorization; authorisation; acknowledgment; acknowledgement; certification; recognition
denial; negation; repudiation; disavowal
to fix; to settle; to standardize; to regularize
stipulation; prescription; provision; regulation; rule
definition
hypothesis; supposition; assumption; expectation; anticipation
judgement; judgment; decision; ruling; finding; adjudication; verdict; call
measurement
sticking (in one place, position, etc.); settling; fixing; adherence
instability; insecurity; crankiness
arrangement; pact; agreement
standard item; usual thing; (a) classic; go-to choice; staple; regular fixture; standard procedure; convention
presumption; assumption
judgement; judgment; expert opinion; appraisal
定 combines 宀 (roof, house) with a lower element that is a simplified form of 正 (correct, straight). The idea is of something being set straight or made correct under a roof, hence 'determine, fix, establish'.
Under a roof (宀), a carpenter uses a level to make sure everything is straight and fixed in place. That act of setting things right is 定: to determine, fix, and establish.
For テイ, imagine a table (テーブル, tēburu) being fixed firmly in place under the roof. The 'tei' sound from 'table' (テイ) helps you remember the reading.