ENGLISH
REFERENCE

unable

adj. · interj.
US //əˈneɪbəɫ// UK //ʌnˈeɪbəl// un·able
  1. 1 not capable (adj.)
    B1 Intermediate

    not able to do something because you do not have the skill, time, or power.

    lacking the necessary power, ability, resources, or opportunity to perform a specific action. Usually followed by a 'to' infinitive.

    Example

    She was unable to attend the meeting because her flight was delayed.

    Example

    Despite several attempts to resolve the technical glitch, the support team remained unable to restore the database before the morning shift began.

    Usage

    Always used with a following 'to' + infinitive; it is never used as an attributive adjective before a noun (e.g., 'an unable man' is incorrect).
    Pitfall
    I am unable of coming to the party.
    I am unable to come to the party.

    The adjective 'unable' must be followed by 'to' and a verb, not 'of' and a gerund.

  2. 2 aviation refusal (interj.)
    C1 Advanced Technical Aviation

    a word pilots use to tell air traffic control they cannot follow an order.

    a standardized radio telephony term used to indicate that a requested maneuver or instruction cannot be safely or legally executed.

    Example

    The pilot told the tower 'unable' when asked to climb to a higher altitude.

    Example

    Upon receiving the instruction to expedite the descent, the captain responded with 'unable' due to the severe turbulence reported at lower levels.

    Usage

    Used as a standalone response in radio communications.

    Teacher's tip

    This is highly specialized jargon; outside of aviation, using 'unable' as a one-word sentence sounds very abrupt or robotic.
    • cannot comply
    • wilco
Etymology 1

From Middle English unable, unabel, unhable, unhabil, equivalent to un- + able.

Etymology 2

From Middle English unablen, equivalent to un- + able.

Word family

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