They translate from the Greek word ὀλιγοπιστίαν
From 3641 /olígos, "little in number, low in quantity" and 4102 /pístis, "faith".
Occurs five times in the NT, each time with Jesus rebuking the problem of failing to hear His voice (cf. Jn 10:3,4,27).
"Little-faith" (3640 /oligópistos) describes someone dull to hearing the Lord's voice, or disinterested in walking intimately with Him. In contrast, the goal of life is to receive (obey) the Lord's gift of faith in each scene of life (Ro 14:23; Heb 11:6).
Answer Source
Etymology of /pístis, "faith"
From πιθ- (pith-), the root of πείθω (peíthō), + -σις (-sis), which remained -τις (-tis) after a dental.
Answer Source
The Usages in the New Testament
Matthew 6:30
Here it gets used as "little convinced". Those that understand the power of God do not need to worry about food, drink, or clothing. Those "convinced" know with certainty that God provides.
Matthew 8:26
Here Jesus rebukes his disciples for if they where convinced, they themselves would have used the word to calm the wind and the seas. However since they were not convinced of the power of what they say, Jesus had to show them again and himself told the wind and seas to calm.
Matthew 14:31
Here Jesus uses the power of the word and told Peter to "Come" meaning to also come walk on the water. Peter upon seeing the wind began to doubt and started to sink, therefore the rebuke.
Matthew 16:8
Here the rebuke comes from a general lack of understanding the metaphor "leaven". Perhaps Jesus uses other metaphors? Just something to think about.
Matthew 17:20
Here again Jesus tries to explain the power of what a person says. That even telling a mountain to move will move a mountain and that nothings impossible for those that believe in the power of what they say. They still remain unconvinced at the power of what we say, therefore he calls them "hardly convinced".
Luke 12:28
Again used to express how we do not have to worry about food, drink, or clothes. That by simply saying what we need, God will provide.
