1 Corinthians 1:23 But we preach Christ crucified, unto the Jews a stumblingblock, and unto the Greeks foolishness;
Romans 14:13 Let us not therefore judge one another any more: but judge this rather, that no man put a stumblingblock or an occasion to fall in his brother's way.
Stumblingblock is from the Greek word "Skandalon" from which we get our English word, "Scandal". Essentially means "an occasion to sin" or that which prevents one from doing what's right.
Here is a definition from Vine's Dictionary of New Testament Words:
skandalon (Strong's number G4625) originally was "the name of the part of a trap to which the bait is attached, hence, the trap or snare itself, as in Rom_11:9, RV, 'stumblingblock,' quoted from Psa_69:22, and in Rev_2:14, for Balaam's device was rather a trap for Israel than a stumblingblock to them, and in Mat_16:23... In the NT skandalon is always used metaphorically, and ordinarily of anything that arouses prejudice, or becomes a hindrance to others, or causes them to fall by the way. Sometimes the hindrance is in itself good, and those stumbled by it are the wicked.
I hope you have found this helpful.