If you'd like to dig more into this, the key word you are looking for is "etymology", the study of word origins and associated issues: http://en.wikipedia.org/wiki/Etymology
If you look in dictionaries, especially the more complete ones, all words will have their etymologies spelled out. For instance, the etymology for etymology from http://www.merriam-webster.com/dictionary/etymology is:
Etymology: Middle English ethimologie, from Anglo-French, from Latin etymologia, from Greek, from etymon + -logia -logy
For pretty much every word you can think of in English, there's a locally-sensible etymology for it. English's problem is the attitude exemplified in the classic quote:
"The problem with defending the purity of the English language is that English is about as pure as a cribhouse whore. We don't just borrow words; on occasion, English has pursued other languages down alleyways to beat them unconscious and rifle their pockets for new vocabulary." - James D. Nicoll http://linguistlist.org/issues/13/13-499.html
The problem isn't that we don't have roots in English; the problem is that we have three-ish major sets of them (Anglo-Saxon, Greek, Latin, though if you really dig those are all somewhat related too, for instance see m-w.com's entry for "fire"), and will freely borrow any others we need at will.
Of course the practical effect for a foreign learner is that it doesn't look like we have roots.
This is why spelling contests in English can actually be interesting. It is also why, at the higher levels of competition, the contestant always asks for the etymology of the word; it isn't just a play for time, though it is that, it is also a vital question! Spelling an Arabic-descended word like "falafel" with Greek phonetics might come out "phalaphel" and that's just embarrassing. (Compare with the phonetics, etymology, and spelling of "phosphor", with its two "ph"s.)
I prefer http://www.etymonline.com/index.php - indeed, I have a keyword search in Firefox set up for just this. Also, see acre's etymology - also cognates in Sanskrit etc., but seemingly more direct than pyre etc.
If you look in dictionaries, especially the more complete ones, all words will have their etymologies spelled out. For instance, the etymology for etymology from http://www.merriam-webster.com/dictionary/etymology is:
Etymology: Middle English ethimologie, from Anglo-French, from Latin etymologia, from Greek, from etymon + -logia -logy
For pretty much every word you can think of in English, there's a locally-sensible etymology for it. English's problem is the attitude exemplified in the classic quote:
"The problem with defending the purity of the English language is that English is about as pure as a cribhouse whore. We don't just borrow words; on occasion, English has pursued other languages down alleyways to beat them unconscious and rifle their pockets for new vocabulary." - James D. Nicoll http://linguistlist.org/issues/13/13-499.html
The problem isn't that we don't have roots in English; the problem is that we have three-ish major sets of them (Anglo-Saxon, Greek, Latin, though if you really dig those are all somewhat related too, for instance see m-w.com's entry for "fire"), and will freely borrow any others we need at will.
Of course the practical effect for a foreign learner is that it doesn't look like we have roots.
This is why spelling contests in English can actually be interesting. It is also why, at the higher levels of competition, the contestant always asks for the etymology of the word; it isn't just a play for time, though it is that, it is also a vital question! Spelling an Arabic-descended word like "falafel" with Greek phonetics might come out "phalaphel" and that's just embarrassing. (Compare with the phonetics, etymology, and spelling of "phosphor", with its two "ph"s.)