Erm, what do you mean by 'like one word' A lot of things are pronounced with a continuos stream of air (interrupted at various times by various sorts of consonant. An English-speaking student will call a distated passage of French 'very fast - with no breaks between the words. A French-speaking student will call a dictated passage of English 'très vite, sans aucune espace entre les mots' (or something like that). It's really quite difficult to provide a satisfactory definition for 'word'.
But I know what you mean, really, and I would probably use the word 'elision' (although elision usually [always] involves a syllable being omitted (as in 'he is' -> 'he's'); and in discussing French (in English) I would use the word 'liaison'.
In print, when one letter is joined to another, that is a 'ligature'. (Both 'ligature' and 'liaison' derive from a single latin root, ligare [='to tie'] - not essential information, I admit, but I find it noteworthy.
Student or Learner