Icelandic builds new adjectives by adding the suffixes -mikill (much/great) or -lítill (little/small) to a noun. This expresses an abundance or lack of a specific quality, similar to English prefixes like "high-" and "low-".
For example, starting with pláss (space), a vehicle with a lot of space is plássmikill (roomy), while one lacking space is plásslítill (cramped).
These suffixes attach directly to noun roots, such as eyðsla (fuel consumption) and viðhald (maintenance).
Declining Compound Adjectives
Like all adjectives, these compounds agree with the noun they describe in gender, number, and case. They decline exactly like the base adjectives mikill and lítill.
When describing a feminine noun like ferð (trip), use the feminine nominative -mikil or -lítil.
When modifying a neuter noun, or making a general statement starting with Það er... (It is...), use the neuter forms -mikið or -lítið.
Finally, pay attention to the masculine accusative form. When a masculine noun like húsbíll (campervan) acts as a direct object, the adjectives agree with it, becoming -mikinn or -lítinn.