furchtbar
terrible
Very bad, awful, or frightening.
Der Film war so furchtbar, dass wir früher gegangen sind.
The movie was so terrible that we left early.

terrible
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terrible
Very bad, awful, or frightening.
Der Film war so furchtbar, dass wir früher gegangen sind.
The movie was so terrible that we left early.

'Furchtbar' (terrible) is derived from the noun 'die Furcht' (fear). The ending '-bar' means something like '-able' or 'full of'. Something that is 'furchtbar' is therefore literally 'fear-inducing' or 'terrible'.
Die Zerstörung nach dem Sturm war ein furchtbarer Anblick.
The destruction after the storm was a terrible sight.
The meaning of 'furchtbar' (terrible / terribly) depends on its position. If it describes a noun, it means 'terrible'. If it stands before another adjective, it intensifies that adjective and means 'very' or 'extremely'.
Wir hatten gestern ein furchtbares Gewitter.
We had a terrible thunderstorm yesterday.
As an intensifying word, 'furchtbar' (terribly) is very popular in colloquial speech. Interestingly, it can intensify both positive and negative qualities.
Dein neues Kleid ist furchtbar schön!
Your new dress is terribly beautiful!
very
'sehr' and 'furchtbar' can both make a statement stronger. 'sehr' is neutral and fits in almost all situations: 'sehr gut' (very good), 'sehr müde' (very tired), 'jemanden sehr mögen' (to like someone very much). 'furchtbar' sounds stronger and often more emotional. As an intensifier, it is more colloquial, for example 'furchtbar nett' (terribly nice) or 'furchtbar müde' (terribly tired). The words can be confused because 'furchtbar' sometimes works like 'sehr'. But 'furchtbar' can also mean 'terrible' or 'very bad'. So 'sehr' is better when you want to speak neutrally and clearly.

Nach dem Unterricht ist ihr furchtbar kalt.
After class, she is terribly cold.
Die Chefin achtet wegen des Wetters sehr auf die Sicherheit der Kinder.
Because of the weather, the boss pays very close attention to the children's safety.