There's no hard and fast rule universally to your answer. In the
given climate, given the way things are, I'd say chuck all
definitions out of the window - it's useless.
Case in point : UBS and Credit Suisse as entities are
effectively commercial banks with both retail and investment
banking operations. That said, you don't expect to find UBS or
Credit Suisse branches in Singapore (or anywhere in the world
outside Switzerland) that deals exclusively with retail
banking (well, exclude PWM which is effectively a branch of
investment banking these days).
In that regard, Credit Suisse and UBS' effective stature in
Singapore is no different from Goldman Sachs and Morgan Stanley
(traditionally pure investment banks and, even though these banks
have since acquired bank holding status, there's nothing to suggest
they'd go into retail banking on the scale of the Citi, HSBC or
BofA - fact of the matter is these banks had to acquire the bank
holding status to gain access to additional liquidity from the Fed
to help them get by).
Morgan Stanley and Goldman Sachs are now subjected to the more
stringent regulations of the Fed (as opposed to the SEC when they
were pure investment banks) as part of the obligations they have to
fulfil to gain the same level of access to the Fed as other
commercial banks.
In short, the more relevant question is - in what context do you
want to address your question?
If you're speaking as an investor and you don't belong to the
high net worth bracket, you hardly need to worry about the
difference between Goldman Sachs and UBS (even though these two
institutions hold different status technically).