"Riddle" has a similar meaning to "sieve", but the two words have different origins.
Both riddle and sieve can be traced back to the language "proto Indo European" that is the ancestor language of most European and North Indian languages. As nobody speaks Proto Indo-European and nobody wrote it down, the language is reconstructed from later languages. Reconstructed words are indicated with an asterisk (*)
Sieve <- Proto-germanic *sib- < Proto Indo-European *seib, which means "pour out", "drip", or "sieve".
The word has changed only slightly over 5000 years, the "b" has become a "v" and the vowel has shifted. On the other hand, riddle has changed quite a lot
Riddle <- Old English "hriddle" <- Proto-Germanic *Hrida- <- Proto IndoEuropean <- *krei-, meaning "sieve".
The same root word *krei-, also gives us the meaning of sort, judgement, and from the meaning "judgement we get the word for things that are judged. The word "crime" has the same origin.
So words that are very different in meanings can have the same origin "crime" and "riddle" have the same origin. Words with similar meanings can have completely different origins. "Sieve" and "Riddle" have similar meanings, but they are not related.
The physical shape of a word on the page has nothing to do with the meaning of a word.