Neoplasm: a tumour, a new growth of tissue which serves no function in the body. Neoplasms can be benign (not cancer) or malignant (cancer).
The word results from the combination of the Greek neo-, meaning “new” (as in “neonatal”, or “newly born”), and -plasma, “something moulded or created” (as in “plastic”). The phenomenon by which a tumour arises is known as “neoplasia”. The adjective is “neoplastic”, which makes it sound like the material smart phones are made of.
Cracked Science 
It is true that doctors like to say ‘neoplasm’ for tumour in order not to scare the patient. However, the two terms are (on a philosophical level) far from synonimous. Neoplasm is, essentially, a product of the process of neoplasia – while this does mean “new growth” in greek, in cellular/molecular biology it primarily denotes an altered pattern of cell growth regulation, as well as failure of communication at the level of cell/organism. This is important because this is a PROCESS, not a thing. And this process may or may not lead to formation of tumours, and those tumours may be less or more malgnant, along a wide continuum, depending on the alterations undepinning the process of neoplasia and myriad factors (diet, lifestyle, stress, immune recognition) that affect the unfolding of this process.
More briefly, to say to a patient that she or he has ‘neoplasia’ is NOT an euphemism for ‘tumour’ or ‘cancer’, but an attempt to convey the (biologically and philosophically) right way to look at the problem – as a complex process.
Thanks for chiming in. I must correct you, however, when you claim in your last paragraph that I equated “neoplasia” with “tumour” (I equated “neoplasm” with “tumour”) and “cancer” (which I never did, clearly stating that a neoplasm can be benign or malignant). You are correct that “neoplasia” is a process, not a thing, but the item I was defining was “neoplasm”; when writing about “neoplasia”, I stated it was a “phenomenon by which a tumour arises”. We seem to agree on this, although your phrasing is much more elegant than mine (I like “process”… it’s better than “phenomenon” in this case). Thanks!