The Greek verb katechō means to hold fast, to hold back, to keep possession of, or to restrain. It is a compound of kata ('down, against') and echō ('to have, hold'). The word appears approximately 18 times in the New Testament with both positive and negative senses: holding fast to what is good, or holding back/suppressing what ought to be free.
Romans 1:18 uses katechō negatively: 'who suppress (katechontōn) the truth by their wickedness.' The deliberate holding down of known truth is the root of Paul's indictment of Gentile idolatry. Truth is not absent but actively suppressed — making humanity culpable.
1 Thessalonians 5:21 and Hebrews 3:6 use katechō positively: 'hold on to the good,' 'hold firmly to our courage and the hope.' The believer is called to katechō what is true and good — to grip it tightly against the forces that would loosen it. The word thus captures both the danger of apostasy and the discipline of perseverance.