In formal speaking or writing, we can use although, though and even though to introduce a clause without a verb (a reduced clause):
Raymond, although very interested, didn’t show any emotion when she invited him to go for a walk.
[referring to a car]
Though more expensive, the new model is safer and more efficient.
When the although/though clause comes after a main clause, it can also mean ‘but it is also true that …’:
Karen is coming to stay next week although I’m not sure what day she is coming.
We didn’t make any profit though nobody knows why.
Though meaning ‘however’
Spoken English:
Especially in speaking, we can use though (but not although or even though) with a meaning similar to however or nevertheless. In these cases, we usually put it at the end of a clause:
A: You have six hours in the airport between flights!
B: I don’t mind, though. I have lots of work to do. I’ll just bring my laptop with me.
A: It’s expensive.
B: It’s nice, though.
A: Yeah, I think I’ll buy it.
As though
As though has a meaning very similar to as if. As if is much more common than as though:
You look as though/as if you have seen a ghost!
He looks as though/as if he hasn’t slept.