Spendthrift, prodigal, profligate, waster, wastrel are comparable when they denote a person who dissipates his resources foolishly and wastefully.
All are more or less pejorative terms but they may differ significantly in emphasis and application.
Spendthrift and prodigal are the most nearly neutral terms and in themselves, as apart from context, carry little suggestion of moral obliquity; they are, however, the members of the group with specific legal applications and are generally applicable when the basic notion is one of unwise and wasteful expenditure usually of material resources (as wages, wealth, or property).
Spendthrift stresses lack of prudence in spending and usually implies imbalance between income and outgo rather than lavishness.
In legal and quasi-legal use the term implies such expenditure in relation to income and resources as are likely to leave the spendthrift and his dependents public charges.
Prodigal (compare prodigal adj under PROFUSE ) is more likely to suggest such lavish expenditure as can deplete the most abundant resources.
In legal and quasi-legal use the term applies specifically to one held legally incompetent to manage his property or to incur debts because of demonstrated incapacity to avoid foolish dissipation of property.
While profligate may imply the habits of a spendthrift, it is more likely to stress such extravagant, even vicious expenditure of one’s personal powers (as of mind and body) that mere economic waste becomes a secondary matter; characteristically it suggests the utmost of debauchery and dissoluteness.
Waster often comes very close to spendthrift in meaning, but it carries a stronger implication of worthlessness than does the former word. It often suggests the habits of a loafer or ne’er-do-well but it is sometimes applied to men of inherited wealth who spend their lives in idleness or in frivolities.
Wastrel, though it often implies the wasting of money and other resources, more often is applied to a good-for-nothing, whether young or old, especially to one who is a drain upon the community; the prevailing implication is that of disreputableness.