Etymologically ஒவ்வொரு is: ஒ + ஒரு ‘one-one’ வ்வ் is inserted due to the Sandhi Rules)
The first letter of the numeral is duplicated to indicate the applicability of the statement to individual members of a set of A’s.
ஒவ்வொரு A without -உம் means ‘various A’s [considered individually]’ and does not necessarily imply that every A is involved.
a) ஒவ்வொரு குழந்தையும் படிக்க வேண்டும் – every/each child must read.
b) ஒவ்வொரு தந்தையும் சுத்தம் செய்ய வேண்டும் – every/each father must clean.
c) ஒவ்வொரு அரசியல்வாதியும் உண்மையை பேச வேண்டும் – every/each politician must speak the truth.
d) ஒவ்வொடு சாமிக்கு ஒவ்வொரு கொயில் உண்டு – There are various temples for various gods.
The addition of -உம் ‘inclusive’ indicates that no member of the set is left out: i.e. that the statement is applicable to each individual member. The noun form is: ஒவ்வொன்றும் ‘each [thing], each one.’ Note again that -உம் comes after any case ending.
எல்லா A-உம் , எல்லாவற்ற A-உம்
Translates as ‘all A’s ‘
Used for irrational A’s
Note that both this construction and ஒவ்வொரு A-உம் can sometimes be translated by ‘every A’: e.g. ‘there are festivals every month’.
Keep in mind, however, that: எல்லா A-உம் refers to the totality, whereas ஒவ்வொரு A-உம் refers to the members of the set of A’s individually considered.