suitable, occasional, rare, qualified, capable
適 centers on a good fit between a person or thing and a situation: being suitable, qualified, or capable for a role. The occasional and rare senses extend from the idea of something fitting only in specific, infrequent circumstances.
適 combines 辶 (movement) with 啇, which likely contributes the sound and relates to hitting a target or fitting exactly. The overall idea is moving toward something that fits.
The movement radical 辶 suggests going somewhere, and the inside part 啇 looks like a target with a mark. Picture an arrow moving along a path and hitting the exact right spot: that is what makes it suitable.
For テキ, imagine a tech expert who is perfectly qualified for the job: tech -> テキ, and their skills fit the role exactly.
suitable; proper; appropriate; adequate; fit; fair
application (of a rule, law, method, etc.)
appropriate; suitable; fitting; apt; proper; right; pertinent; relevant
pleasant; agreeable; comfortable
most suitable; optimum; optimal; best
adaptation; accommodation; conformity
reasonable; suitable
to fit; to suit
conformity; compatibility; adaptability; congruity; congruence
unsuitable; inappropriate; improper
moderate (degree); proper (amount); temperate; suitable
aptitude; aptness; suitability
eligible; qualified; competent
proper quantity; suitable amount; proper dose; optimal dose
non-conforming process; noncompliant; incompatible
to suit (one's needs, tastes, purpose, etc.); to serve; to meet (one's expectations, wishes, etc.); to measure up to (e.g. one's ideal); to conform to (the law, standards, etc.); to be consistent with (reason, morality, etc.)
suitable; appropriate; fitting; proper
timely; opportune
legal; lawful; legitimate
competent; suitable; qualified