Lily Tomlin plays the title role in "Grandma," Paul Weitz's comedy-drama about a meek high schooler, Sage (Julia Garner), who learns a thing or two from her feminist grandmother, Elle. They're on a mission: Elle is helping young Sage raise the cash for an abortion.

Clearly, "Grandma" is not your usual movie about family bonding. It isn't even your usual movie about abortion. You won't hear much agonizing over the idea, especially not from Elle. She gives Sage one warning -- "This is something you'll probably think about every day for the rest of your life" -- and that's the extent of any moralizing.

All of which makes "Grandma" a very daring film, even by the standards of edgy movies like "Juno" and "Citizen Ruth," which also tackled this touchy subject. Screenwriters generally punt on abortion; one common exit strategy is to grant the heroine a last-minute, guilt-free miscarriage. No spoilers on Sage's ultimate decision, but "Grandma" comes at its topic head-on and with no apologies.

When the film works -- which is about half the time -- it's because of Tomlin, perfectly cast as a foul-mouthed, punk-rock lesbian poet (Judy Greer plays her much younger girlfriend, Olivia). Tomlin looks a bit like Patti Smith: ratty denim jacket, wild hair, a face lined by experience. As Elle drives around town trying to coax money from old bohemian friends (a tattoo artist played by Laverne Cox, a cafe owner played by the late Elizabeth Peña), it's clear that Elle is far cooler and tougher than her pushover granddaughter. After all, Sage is the one who slept with Cam, a callous dolt played by Nat Wolff ("Paper Towns").

Weitz, whose comedy credits include "American Pie" and "About a Boy," seems slightly in over his head with "Grandma." He gets distracted from his theme by currently trendy topics like modern sexuality (Elle's ex-husband is played by Sam Elliot) and nontraditional families (Marcia Gay Harden plays Sage's mother, Judy, who was raised by Elle and another woman). That, plus some patches of overly pointed dialogue, keep the film from feeling properly focused and fully convincing. Nevertheless, "Grandma" deserves credit for looking squarely at a subject that most films would rather avoid.

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Four more: Lily Tomlin's grandmother predecessors

Oh, Grandma, what a sassy mouth you have! Lily Tomlin plays the super-feisty title role in "Grandma," which opens on Long Island Friday. Here are four of her big-screen ancestors who also played slightly naughty but still nice nanas.

A STAR IS BORN (1937) -- Farm girl Janet Gaynor dreams of being a movie star, but it's not until her no-nonsense grandma (May Robson) gives her an inspiring pep talk and her life savings that she grabs the next train to Hollywood.

GRANDMA'S BOY (2006) -- Doris Roberts played an edgier version of her character from "Everybody Loves Raymond" as Adam Sandler's granny in this raunchy comedy, in which she and her geriatric pals (Shirley Knight, Shirley Jones) have some high times after drinking a strange brew that they think is herbal tea.

THE PROPOSAL (2009) -- Sandra Bullock and Ryan Reynolds starred in this rom com, but the movie's most engaging presence was Betty White as Reynolds' grandma, whose big moment came doing an amusing tribal Eskimo dance.

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TAMMY (2014) -- "Thelma and Louise" star Susan Sarandon played Melissa McCarthy's beer-swilling grandmother -- who may have had a fling with one of the Allman Brothers -- in this lighter and randier spin on the 1992 female road-trip drama.

--Daniel Bubbeo