hit, right, appropriate, himself
当 centers on the idea of something making direct contact or aligning correctly: hitting a target, being right or appropriate, and by extension, referring to the person or thing itself that is directly involved.
really; truly
truth; reality; actuality; fact
being in charge (of an area of responsibility); being responsible (for a work role, etc.)
at that time; in those days
natural; right; proper; just; reasonable; appropriate; deserved
to be hit; to strike
corresponding to (in meaning, function, etc.); being equivalent to
natural; reasonable; obvious
hit
being elected
day in question; appointed day; that very day; the day (of issue, publication, etc.)
suitable; proper; appropriate; adequate; fit; fair
aim; object; purpose; end
beginning; start; outset
bento; Japanese box lunch
corresponding to; being applicable to; being relevant to; coming under; falling under; fulfilling (requirements); meeting (conditions); qualifying for
just; justifiable; right; due; proper; equitable; reasonable; legitimate; legal; lawful
authorities; relevant authorities; authorities concerned
mark; guide; landmark
person concerned; interested party; related party
salary; pay; compensation; allowance (e.g. housing allowance); benefit; bonus
to hit
valid; proper; right; appropriate; reasonable
having in mind; happening to know (of); idea (of); inkling
当 is the modern simplified form of 當. The older form combines 田 (field) and 尚 (which likely contributed the sound), expressing the idea of a field being directly opposite or matching something. The modern form is a simplification that retains the general shape.
The top ⺌ looks like a small target, and the bottom 彐 resembles a hand or tool reaching toward it. Picture an arrow hitting the bullseye: that's a direct hit, exactly right and appropriate.
For トウ, imagine a toe hitting the target perfectly: toe -> トウ, and the direct hit is right on the mark.