find the 7 letter word.

Well I had to think WAY outside the box, but this was all I could come up with:

"Myotome"

"1+3+5+7=animal name" - Since cows go "Moo", a cow could be called a "Moo-e"!

"2+3+4=mode of transportation" - A yacht (pronounced "yot") is a form of transportation.

"4+5+6=essential to live" - I order for life to continue, it would be essential that we see tomorrow ("tom")!

"6+7=pronoun" - "me" is a pronoun.

Ha ha!